The present invention is directed to a hydraulic controlled well valve for use in a well conduit controlling fluid flow between the inside of the conduit and the outside of the conduit such as the well annulus. The valve is operated by a single hydraulic control line to the well surface. The piston is subjected to differential pressure between the control line pressure and the annulus fluid whereby the valve does not have to overcome hydrostatic head forces for closure and therefore is not limited in its setting depths. In addition, the seals to the bore are equal whereby the valve will not be influenced by bore or tubing pressure. The valve is a sliding valve type which achieves maximum flow area by utilizing one side of the sealing area against the well conduit thereby eliminating one tubular wall for increasing flow area capabilities. The valve may be wireline retrievable and be set in a sidepocket mandrel or in a nipple in the well tubing.